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Computing in Security (Conversion Help)

1.) Express each decimal number as an 8-bit binary number in the 2's complement form and then find the negative of the representation of that number in two’s compliment

a.) +18

b) -117

Thanks for any help!

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asked by Francesca

  1. Two's complement is a notation that represents both positive and negative numbers. The most significant (left-most) is the sign bit, which is turned on when the number is negative.

    Unlike the one's complement, there is only one representation of zero.

    For an eight-bit number, the range goes from -128 to 127.

    A positive number is represented by a usual binary number format, using the 7 low-order (right-most) bits, and represent from 0 to 127.

    A negative number is simply the reversal of the bits and then add 1.

    Example:
    10(decimal)=00001010(binary)
    -10(decimal)=11110101 + 1
    =11110110

    18(decimal)=00010010(binary)
    -18(decimal)=11101101 + 1
    =11101110

    and so on.

    To negate a negative number, subtract one and reverse the bits.

    For example,
    -18(decimal)=11101110
    subtract 1
    11101101
    Reverse bits
    00010010 (binary -18)

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    posted by MathMate

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